Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel injection, or delivery, uses a port injector for each cylinder to deliver fuel to respective cylinders. Another type of fuel injection uses a direct injector for each cylinder. Engines have also been described using more than one injector to provide fuel to a single cylinder in an attempt to improve engine performance.
One such example is described in US 2007/0215110 wherein a flexible multiple-fuel engine is described using both port and direct injection, where different fuel types are provided to the injectors. For example, direct injection of ethanol may be used with port injected gasoline. The direct injection of ethanol provides improved charge cooling (due to ethanol's higher heat of vaporization) and thus improved knock suppression. One embodiment controls fuel injection responsive to a variety of temperature-related engine operating conditions during engine start-up. For example, during start-up, fuel injection may be varied among the different injection locations to provide improved emission control and starting of combustion.
However, the inventors have herein recognized a potential issue with such an approach. For example, while different fuel adjustments can better accommodate warming and start-up conditions, there may also be over-temperature conditions at non-starting conditions. In other words, catalyst over-temperature is generally not an issue during starting. Rather, during towing and/or other high load conditions over varying terrain, catalyst over-temperature conditions may occur and degrade the catalyst materials.
In one example, the above issues may be addressed by a method of operating an engine in a vehicle, the method comprising: delivering a first substance to a cylinder of the engine from a first injector; delivering a second substance to the cylinder of the engine from a second injector, where the second substance has a greater heat of vaporization than the first substance; and increasing injection of the second substance responsive to an exhaust over-temperature condition.
In this way, it is possible to address exhaust over-temperature conditions by preferentially utilizing the increased heat of vaporization of the second fuel. Such an operation may be especially advantageous when the second substance is directly injected into the cylinder, since the fuel spray may not contact metal surfaces of the engine, so virtually all the heat of vaporization is provided by the air-fuel mixture, thus reducing exhaust gas temperature in addition to combustion temperature. Additionally, such an operation may be particularly useful when exhaust equivalence ratio is maintained near the stoichiometric ratio, since emission impacts of catalyst temperature protection may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.